The invention is related to an asymmetric angular contact bearing, comprising an inner ring and an outer ring each defining a raceway, at least one ring being provided with a high shoulder and a low shoulder which border the raceway of said ring, as well as a series of rolling elements which are in rolling contact with the raceways.
Such bearing, e.g. a ball bearing, roller bearing or cross roller bearing, is generally known. The different contact angles of its asymmetric contact lines make the bearing suitable for carrying relatively high axial loads in one direction.
This property is of importance for specific applications of the bearing, in which the main axial loading always has the same direction. Examples of such application are screw actuators, used in for instance brake callipers for brake discs. In such cases, the main axial loading concerned is related to the displacement of the brake pads onto the brake disc. The opposite displacement is for relieving the braking action between brake pads and brake disc, and gives rise to loadings of a much lower magnitude.
Another example is the application of such bearing in a clutch.
The object of tile invention is to provide an asymmetric angular contact bearing, which is more versatile as to assembling and layout and can be produced at lower cost (no split rings). This object is achieved in that the low shoulder is provided with a circumferential groove, a ring member being accommodated in said groove or contacting the rolling elements.
The asymmetric angular contact bearing according to the invention has, as is the case with prior art angular contact bearings, two contact points between each rolling element and each of the rings, which accumulates to a total of four contact points for each ball. Thus, the rings on the one hand, and each rolling element on the other hand engage each other at four contact points, two contact lines being defined by the two pairs of diametrically opposite contact points, one of said contact lines defining a contact angle with respect to the axis of the bearing which is relatively small, and the other contact line defining a contact angle with respect to the axis of the bearing which is relatively large.
Distinct from the prior art bearings, one of said contact points of each ball is constituted by the ring clement according to the invention. The ring element provides several advantages concerning assembling and lay-out of the bearing, which will be addressed in the following.
Rolling element bearings having ring elements or ring-shaped inserts are known per se. GB-A-1007191 discloses a bearing having a total of four ring elements, each constituting one of the contact points of a rolling element. However, said prior art bearing is not an asymmetric angular contact bearing, nor do the rings thereof have a high shoulder and a low shoulder. Said bearing is not fit for relatively high axial loading.
A further example of a prior art rolling element bearing is disclosed in EP-A-245593. This bearing neither is an asymmetric angular contact bearing, nor do its rings have a high shoulder and a low shoulder. The bearing in question may be carried out as a radial ball bearing or as a cross roller bearing.
In order to obtain the desired axial load bearing capacity, the bearing according to the invention is carried out in such a way that one contact line is defined by the contact point of the ring member and a rolling element, and by the contact point of the shoulder diametrically opposite to said ring member and said rolling element, said contact line having a relatively large contact angle.
The main axial load is to be carried by the shoulders which define the other contact line, which has a relative small contact angle.
Preferably, the low shoulder, which is provided with a groove, has an internal cylindrical surface the diameter of which is equal to the maximal diameter of the raceway. This embodiment has the advantage of an easy and straightforward assembly. This advantage offers the possibility to assemble the bearing as a full complement bearing, wherein the available bearing space between the rings is fully occupied by rolling elements, without a cage. The balls are put into place by simply sliding them past the low shoulder, after which they are secured by means of the lock ring member.
The low shoulder may be equipped with a seal or shield. The pair of shoulders opposite the pair of shoulders one of which has a ring member, enclose a gap defining a labyrinth seal. Sealing can also take place with a seal or shield.
The ring member may have a generally round or circular cross section. Alternatively, the ring member at its surface part facing the rolling elements, may at least partly be conformed to the shape of said rolling elements.
The invention is also related to a screw actuator, comprising a screw mechanism, a housing with or without a gear reduction and an asymmetric bearing as described before, comprising an inner ring and an outer ring each defining a raceway, at least one ring being provided with a high shoulder and a low shoulder which border the raceway of said ring, as well as a series of rolling elements which are in rolling contact with the raceways, said bearing supporting one of the nut and screw of the screw mechanism with respect to the housing, the outer ring of the bearing engaging the screw of the screw mechanism.
The bearing according to the invention may in particular be applied in such screw actuator, as explained before, in case said actuator is mainly exposed to axial loadings in one and the same direction, e.g. as applied in a brake calliper for a disc brake. To that end, the low shoulder of the bearing is provided with a circumferential groove, a ring member being accommodated in said groove for contacting the rolling elements.
In a particular embodiment, the inner ring of the bearing may engage, or may be integrated in, a central support shaft connected to the housing of the actuator.
Preferably, the screw mechanism is a roller or ball screw, the nut of which is carried out as a sleeve or piston which is slidably but non-rotatably accommodated in a cylinder space in the housing.
According to a further possibility, the bearing according to the invention may be applied in a screw actuator, comprising a screw mechanism, a housing and an asymmetric bearing, comprising an inner ring and an outer ring each defining a raceway, at least one ring being provided with a high shoulder and a low shoulder which border the raceway of said ring, as well as a series of rolling elements which are in rolling contact with the raceways, said bearing supporting one of the nut and screw of the screw mechanism with respect to the housing, the inner ring of the bearing engaging the nut of the screw mechanism.
Here as well, the low shoulder is provided with a circumferential groove, a ring member being accommodated in said groove for contacting the rolling elements.
Preferably, the outer ring is supported with respect to the housing, and the screw is axially displaceable, but non-rotatable.